Asymmetrical phenolic nondiscoloring antidegradants for polymers



United States Patent 3,505,287 ASYMMETRICAL PHENOLIC NONDISCOLORING ANTIDEGRADANTS FOR POLYMERS Evan Johnson Young, St. Albans, and Charles Gene Summers, Scott Depot, W. Va., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Jan. 16, 1967, Ser. No. 609,335 Int. Cl. C08c 11/30 U.S. Cl. 260-4535 12 Claims ABSTRACT OF THE DISCLOSURE Compounds of the formula where R is secondary or tertiary alkyl and X is straight or branched chain primary, secondary, or tertiary alkyl, are excellent non-discoloring antidegradants for rubber polymers. Mixtures containing isomers of these compounds are also excellent non-discoloring antidegradants.

BACKGROUND OF THE INVENTION The invention pertains to the field of antidegradants for olefin and diolefin polymers. Certain specific hydroxy compounds are known antidegradants. Known hydroxy compounds include bridged cresols of which the compound 4,4'-butylidenebis(6-tert-butyl-m-cresol) is a rubber antioxidant trademarked Santowhite powder. Santowhite powder is a member of a family of antioxidants prepared by reacting a 2,5-dialkyl phenol with an aldehyde. The number position and kind of alkyl strongly influence antioxidant efficiency. Reacting aldehydes with dialkyl phenols having the alkyl groups in positions other than the 2- and 5-position may result in compositions not useful as antioxidants according to Beavers U.S. Patent 2,816,945 of Monsanto Company (1957). Ambelang studied the reaction of 2,5-dialkyl phenols with aldehydes to produce 4,4-alkylidene-bis(6-tert-alkyl-m-cresols). The Structure and Configuration of Dihydroxydiphenylmethanes Derived From Butylated mCresols as Evidenced by Infrared Absorption, Journal of the Americal Chemical Society 75,947 (1953). He suggests the existence of unsymmetrical bis-6-tert-aikyl-m-cresols in which the alkylidene bridge is in the 2-position in one ring and in the 4-positi0n in the other. No use for the products is disclosed. The compound 4-hydroxymethyl-2,6-di-tert-butyl-phenol is a rubber antioxidant trademarked Ionox 100. The compound 2,6-di-tert-butyl-4-methyl phenol is a rubber antioxidant. trademarked Ionol. British Patent 927,179 of the Ethyl Corporation published May 29, 1963, discloses methylenebis phenols and their use as antioxidants having at least one tertiary alkyl group of 4 to 9 carbon atoms positioned ortho to hydroxy and at least one hydroxy positioned para to the methylene bridge. Insofar as the patent discloses methylenebis dialkyl phenols, all 4 alkyl groups are adjacent to hydroxy or three of them are adjacent to hydroxy and one para to hydroxy. The compound 4,4- methylenebis(2,6-di-tert-butyl phenol) is a rubber antioxidant trademarked Ethyl Antioxidant 702. The compound 2,2'-rnethylenebis(4-methyl-6-tert-butyl phenol) is an antioxidant trademarked Antioxidant 2246. In the methylenebis 2,4-dialkyl phenols, it is pointed out by Davis 3,505,287 Patented Apr. 7, 1970 that increasing the size of the methylene bridge adversely affects the activity of the compound as an antioxidant. U.S. Patent 2,538,355 of the American Cyanamid Company (1951).

An antidegradant which is non-discoloring to a polymer and has good stabilization against oxygen degradation is necessary for raw polymers. The compound and compound mixtures of our invention display both of these properties. They are at least equivalent to the most effective prior art compounds in both properties and superior in one.

SUMMARY Compounds of the formula 0H CH,

X i RA*(IJ c in R where R is secondary or tertiary alkyl and X is straight or branched chain primary, secondary, or tertiary alkyl, are excellent non-discoloring antidegradants for rubber polymers. Mixtures containing isomers of these compounds are also excellent non-discoloring antidegradants.

In the rubber industry it is customary to add an antidegradant during compounding of vulcanizable stocks. Polymers obtained by solution or emulsion polymerization must be protected immediately after polymerization because they may be stored in bales of raw polymer for a month or more before the polymer is compounded and cured for consumer use. The baled polymer must contain a stabilizer to prevent degradation. When consumer use is for a white pigmented or non-filled polymer product, the baled raw polymer is useless for this purpose if it has become discolored. The use of compounds or mixtures of this invention in raw polybutadiene provides a non-discolored polymer with good stabilization against oxygen degradation. The use of compounds or mixtures of this invention in raw polybutadiene is an improvement over the prior art.

Antioxidant 2246 discolors polybutadiene during aging. Santowhite powder is essentially non-discoloring in polybutadiene but is derived from the relatively scarce and expensive meta-cresol. The new bridged cresols are nondiscoloring to the baled raw polymer and more effective stabilizers than Santowhite powder. At the same time economy in production is achieved. The most economical antioxidants comprise compound mixtures which contain as essential ingredients the new unsymmetrical bridged cresols.

An example of the new compound is 2-[alpha, alpha-f4- hydroxy Z-methyl-S-tert-butyl phenyl)butyl ]-6tert-butylp-cresol of the formula C II;

The mixtures containing the new compounds may be prepared by reacting a mixture of -alkyl-m-cresol and 2-alkyl-p-cresol with an aliphatic aldehyde of 2 to 7 carbon atoms. For example, mixtures of compounds obtained when about 2 parts of alkylated m-cresol and 1 part of alkylated p-cresol are bridged with an alkylidene group of 2 to 7 carbons, and in which the alkyl group on the cresols contains from 4 to 12 carbon atoms are excellent stabilizers. An example of this type of mixture is the reaction product obtained when a mixture of tertbutyl-m-cresol and tert-butyl-p-cresol is bridged with n-butyraldehyde. This mixture contains 2,2'-butylidenebis(6-tert-butyl-p-cresol), 4,4'-butylidenebis(6-tert-butylm-cresol) and 2-[alpha, alpha-(4-hydroxy-2-methyl-5- tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol.

PREFERRED EMBODIMENTS To prepare 2-[alpha, alpha-(4-hydroxy-2-methyl-5-tcrtbutyl phenyl)butyl]-6-tert-butyl-p-cresol, 82 grams (0.5 mole) of Z-tert-butyl-p-cresol and 82 grams (0.5 mole) of 6-tert-butyl-m-cresol are charged into a gas sparger equipped reaction flask. Methanol (100 ml.) is added and gaseous hydrogen chloride (0.4 mole) is fed into the stirred solution for about 1 hour. Forty grams of n-butyraldehyde (0.56 mole) is added in 1 hour at 45 C. The reaction mixture is stirred an additional 2 hours at 6070 C. The reaction mixture is cooled to 30 C. and 100 grams of water is added and the mixture is stirred. After stirring for 5 minutes, the aqueous phase is decanted. The organic phase is washed with two 150 gram portions of water. At this stage of the process, the batch may be steam sparged to remove residual tert-butyl-m-cresol and tert-butyl-p-cresol. The reaction product contains about 41% 2-[alpha, alpha-(4-hydroxy-2-methyl-5-tertbutyl phenyl)butyl]-6-tert-butyl-p-cresol, about 27.7% 4,4'-butylidenebis(6-tert-butyLm-cresol). and about 26% 2,2-butylidenebis(fi-tert-butyl-p-cresol). The product mixture is slurried in 100 grams of hydrocarbon solvent and filtered to remove 4,4-butylidenebis(6-tertbutyl-m-cresol). The filtrate is warmed to 3040 C. and treated with about 5 grams of Super Piltrol clay for decolorization. Filtrol is a trademark for chemically treated colloidal clay for decoloring and purifying. The mixture is filtered and the filtrate is vacuum stripped up to about 100 C./30 mm. Hg. The product is recrystallized with a hydrocarbon solvent to isolate the compound 2-[alpha, alpha-(4-hydroxy-2-methyl-5-tert-butyl phenyl)butyl]-6-tert-butyl-pcresol. Twenty-seven grams of the white solid compound is obtained. The melting point of a sample recrystallized twice in hydrocarbon solvent is l30l3l C. The empirical formula of the compound is C H O The molecular weight is 382.59. The compound elutes at 260 C. on a programmed vapor phase chromatograph when 4,4'-utylidenebis(G-tert-butyl-m-cresol) elutes at 270 C. Other compounds of this invention are prepared in a similar manner to the preparation described above. 1

The mixtures from which the compounds of this invention are isolated are valuable antioxidants. However, it is preferred to employ a higher ratio of 6-tert-butyl-mcresol to decrease discoloration problems in the polymer. Also, mixtures of mand p-cresols in a ratio of about 2:1 are available from coal tar fractions and are economical to use.

Essentially non-discoloring economical mixtures of compounds comprise by weight to 50% 4,4-all ylidenebis(fi-tert-alkyl-m-cresol). 10 to 2,2'-alkylidenebis(6- tert-alkyl-p-cresol), and to 2-[alpha, alpha-(4- hydroxy-Z-methyl-S-tert-alkyl phenyl)alkyl]-6-tert alkyl-pcresol. Antioxidant efiiciency and safety from discoloration are improved by isolating and using the last named component but in most instances the mixtures are satisfactory. The first named component is insoluble in petroleum hydrocarbon solvents. The major portion of it can be removed by treating the reaction product with a petroleum hydrocarbon solvent and removing undissolved solids by filtration. The mixtures of this invention are prepared in a similar manner to the preparation described above. The ratio of the cresols may vary.

An example of a mixture preparation is the reaction of 2 parts of tert-butyl-m-cresol and 1 part of tert-butylp-cresol with n-butyraldehyde. The mixture product of this reaction contains about 14% 2,2-butylidenebis(6-tertbutyl-p-cresol), about 48% 4,4'-butylidenebis(6-tert-butylm-cresol), and about 42% 2[alpha, alpha-(4-hydroxy-2 methyl-S-tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol. In a vapor phase chromatographic analysis of the mixture, the elution time for 2,2'-butylidenebis(G-tert-butyLpcresol) is three minutes, for 2-[alpha, alpha-(4-hydroxy- 2-methyl-5-tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol is 4.15 minutes, and for 4,4-butylidenebis(6-tert-butyl-mcresol) is 6.15 minutes. The analysis is carried out in a four foot column with a inch diameter. The column is packed with 3% silicone gum rubber (trademarked SE52) on Chromosorb W. Chromosorb W is a trademark for a white diatomaceous earth support. The temperature of the column is 260 C. The carrier gas is helium. The flow rate of the helium is ml./minute.

A mixture of this invention is prepared by alkylating 2 parts of m-cresol and one part of p-cresol with Gulf Propylene Trimer. Gulf Propylene Trimer is a narrow boiling Cg olefin fraction obtained from the catalytic p0- lymerization of propylene. It is a liquid highly reactive monooletin, low in peroxides and sulfur, and suitable for alkylation and other olefinic reactions. Alkylation is effected by heating 10 gram mols. of the cresol mixture, 12.5 gram mols. of propylene trimer, and 104 grams of Retrol, an acid activated absorbent clay, at l08l30 C. The reaction is continued until 68% conversion to alkylate and then the reaction mixture is distilled. The mixture of 6-nonyl-m-cresol and 2-nonyl-p-cresol, B.P. 188"- 200" C./30 mm. Hg, is bridged with n-butyraldehyde in the manner previously described. Products prepared by alkylating mixtures of mand p-cresol upon. condensation with an aldehyde yield mixture of this invention substantially identical to those prepared from mixtures of pure alkyl-m-cresol and pure alkyl-p-cresol.

Stabilizers of this invention are mixed with raw solution or emulsion polymers while the polymers are in their dissolved or emulsified state. Solvent is evaporated from the solution polymer at room temperature. The solution polymer can be steam distilled to remove solvent. In steam distillations, lower boiling antidegradants such as Ionel often distill out of the polymer. It is advantageous to use compounds or mixtures of this invention when steam distillation is used because they do not distill out of the polymer. The emulsion polymer is isolated from water by coagulation. The polymers are then milled at 50 C., blended nine times at a mill setting of .008 in., then sheeted out between A.; and inch thickness. The sheets are cut into 25 to 30 gram samples and aged in a covered pan. Color and Mooney Viscosity data are obtained from these samples.

The stability of raw polymers wherein the compounds or mixtures of this invention are used as measured by the change in Mooney Viscosity. The Mooney Viscosity Test has the American Society for Testing Materials Designation, D1646-63. The data below illustrate aging of raw polymers with and without the stabilizers of this invention. Data for known antioxidants are included for comparison purposes.

Color is evaluated by visual observation. In color tests, the most desirable color is colorless. The code for the color characteristics in the tables below is as follows:

C=Colorless LY=Light yellow VLY:Very light yellow A=Amber LA Light amber VLA=Very light amber B=Equal to untreated polymer In some instances the rubber itself is colored and B designates that the treated polymer is equal to the untreated control. Company X, Company Y, and Company Z in the tables stand for commercial polybutadiene from different manufacturers. The unstabilized polybutadiene cements of Company X and Company Y are light amber color. Company Zs unstabhzed polybutadiene ce- The polybutad1ene stocks 111 Table IV contain the folment is colorless. lowing:

TABLE I.POLYBUTADIENE AGING, 100 C.

Polybutadlene CompanyX Company Y Aging time, Mooney Color, Mooney Color, Compound at 0.5 1111". hrs. viscosity 48 hrs. viscosity 48 hrs.

Antioxidant 2:346 44 42 42 37 41.5 DA 37 DA 48 42 2,%' butglidc1nobis ()4-methyl- 0 443g 42 artuty pheno 16 26 30 44 A 29 DA 48 46 47 Mixture of this invention 0 45. 5 42 10 36.5 B 38 B 30 46. 5 37 48 53 55 2-ialpha, alpha'M-hydroxy-2- 0 45. 5 43 mathyl-5-te1't-butylphenyl) 10 37.5 B 31 B butyl]6-tert-butyl-p-cresol. 30 42. 5 34 48 55.5 39 Santowhite powder 0 45.5 43

16 B 45 B 30 53 56 48 68 71 Blank 00 1 I" 30 48 l) idenebis (6-tert-butylm-cresol) 1 Crumbled on mill.

The polybutadiene stocks in Table 11 contain the following: 30

Stock:

l Mixture of this invention containing 17% 4,4 butylidenebis(6 tert butyl m -cresol), 18% 2,2 -butylidenebis(6-tert-butylr p-cresol), and 55% 2-[alpha,alpha-(4-hydroxy 2 methyl 5 tert butyl phenyl) butyl 1 -6-tert-butyl-p-cresol. 2 Antioxidant 2246. 3 2 [alpha,alpha (4 hydroxy 2 methyl- 40 5 tert butyl pheny1)butyl] 6 tertbutyl-p-cresol. 4---- Santowhite powder. 5 Ionol. 6 Blank.

TABLE I1.COMPANY z POLYBUTADIENE AGING Al 70 c- 45 Stabilizer at 0.5 phr... 1 2 3 4 5 6 Mooney Viscosities at 100 C. after aging at 70 0.101-

Initial 55 55 55 54 55 55 2 days--. 55 55 56 56 100 5 days 58 55 57 58 57 140 10 days 54 54 51 a2 59 158 Color of Polybutadiene after aging at 70 C. 1'01- initial C o c o c c Zdays C c c o o VLY-U 55 5days o VLA u c 0 Y 10 days 0 LA 0 0 C Y Samples of polybutadiene containing compound 2-[alpha,alpha (4 hydroxy 2 methyl 5 tert buty] phenyl)butyl]-6-tert-butyl-p-cresol and Ionel were aged 60 at 100 C. for 10 days. The data in Table III illustrate that Company Ys polybutadiene survived even this severe treatment when this compound of our invention is used.

Stock 1 contains 2-[alpha, alpha-(4-hydroxy-2-methyl- S-tert-butylphenyl)butyl]-6-tert-butyl-p-cresol, and stocks 2 and 3 contain Ionol.

TABLE III 1 2 3 Stock... Mooney viscosities at C. after Aging at 100 C. Ior- Initial s7 37 36 5 days 71 154 153 10 days 113 Bl'ittle 1 The sample was too brittle to test.

4,4 butylidenebis(6 tert-butyl-m-cresol), 18% 2,2 butylidenebis(6 tertbutyl p cresol), and 55% 2 [al ha, alpha (4 hydroxy 2 methyl 5 tert butylphenyl)butyl] 6 tert-butylp-cresol.

TABLE IVFCOMPANY Z POLYBUTADIENE AGING AT 70 C.

Stabilizer at 0.5 phi 1 2 3 4 5 ti Mooney viscosities at 100 C. after aging at 70 C. for

Initial 49 4! 40 48 48 4S 57 50 [i1 40 56 53 SS 53 143 4'.) 70 60 Color of polybutadinne alter aging at 70 C. for- [nitial C C C C G C i (l C 0 LA 0 C 10 days C C LY LA C C The compounds and mixtures of this invention are useful antioxidants in cured polymers. The data in Tables V and VI illustrate White natural rubber vulcanizates containing 2 [alpha, alpha (4 hydroxy 2 methyl 5 tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol and mixtures of this invention compared to a blank and Santowhite powder. The natural rubber vulcanizates in Tables V and VI contain the following:

Parts Pale crepe rubber 100.0 Zinc oxide surface treated with propionic acid 25.0 Titanium dioxide filler 50.0 Stearic acid 1.0 Antioxidant 2.0

The ozone data in Table V indicate the time to 80% retention during dynamic ozone exposure. The method used 7 for measuring the ozone damage to vulcanized rubber is described by Decker and Wise, The Stress Relaxation Method for Measuring Ozone Cracking, Rubber World,

April 1962, page 66. The Ultimate Tensile Strength data in Tables V and VI are in pounds/infi. The samples are aged in an aluminum block at 100 C.

TABLE V Ultimate Tensile Strength ()zone to 30') lunged At 24 hrs. At 48 hrs. rotentioti Blank 3, 501) 2, 600 1,800 50 Z-inlpha. olpl1at4-liydroxy-B-methyl-S- tert-butyl phenyl) butyH-ti-tcrt-butyl-p- Cl't'SOl 3, 400 2. HUG L, tint) 4 Santowhito powder. 3, 500 .2, 800 slit) 4;! Mixture of this invention 1 3, 501) 3, 100 2. 400 59 1 The mixture contains 1%; 2 2-IJutylidiene-lJistti-tertbutyl-p-eresul), 53% 2-lalpha, all)litl.-(4-ilydlfl .Z-lnethyi-fi-turt-butyi phenyDbutyll-titort-Inttyl-p-eresol, and 17% 4.4'-uutylidelie-bisttttert-lnityi-in-crusol).

2 The. mixture contains 13.7% 2..-butylidenebis(ti-turt-butyl-p-cresoli. 41.6% 2-[nlplia til11h:i-t l-ltydruxyQ-methyl--tvrt-ln1tyl phenyDhutyH-G- tort-butyl-p-ervsul, and 489;. 4,4-but 'lidt-nol'istti-tnrt-butyl-In-cresol).

TABLE VI Ultimate tensile strength Mixtllrv of this invention containing the rr-nr-tiuu lll'Ot'lltl. ol 2 parts In-cresol and l pnrt D-CiPSUi alkylntvd with Unit Propylene 'lrinur and bridged with n-lntttraldelndu.

2 Mixture of th invention containing 17%, 4.4'-butylident l)is-([Hvl'tbntyl-nl-crvsol), 18% liutylidenvbis (ti-[Pl t-l1ut yl-pcresol), and 559;, 2-inlpha. alphmH-hydl'oxy-lhnetliyl-5-tt*rt-bntyl plienylfllutyli-ti-teltbntyl-p-crt'sol.

The word nikyl which defines R on the alkylated cresoi includes cycloalkyl for purposes of this invention. For example, mixtures of cycloalkylated m-cresols and cycloalkylated p-cresols can be used as starting materials for the bridged compounds and mixtures of this invention. Examples of such starting materials are cyclohexyl m, pcresol and cyciooctyl, m, p-cresol.

The antidegradants of this invention are effective in polymers at concentrations of 0.25 to 10.0 parts per hundreds. Concentrations from 0.25 to 3 parts per hundred are preferred. Comparable results to those in the tables, supra, demonstrating utility are obtained with antidegradants of this invention which are not illustrated. The antidegradants of this invention may be used in homopolymers, copolymers, and terpolymers of olefins, diolefins, and related monomers. Antidegradant properties comparable to those illustrated in polybutadiene and natural rubber are obtained in other polymers, for example styrenebutadiene rubber, butyl rubber, ethylene-propylene diene monomers, polyethylene, polypropylene, and copolymers of butadiene with other monomers such as styrene acrylonitrile, isobutylene, or methyl methacrylate. The foregoing illustrate alpha mono-olefin polymers, synthetic diolefin polymers and natural rubber.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

We claim:

1. A polymer selected from the group consisting of alpha mono-olefin polymers, natural rubber, and synthetic diolefin polymer rubber containing a stabilizing amount of an antidegradant compound of the formula wherein R is secondary or tertiary alkyl of 4 to 12 carbon atoms and X is straight or branched chain primary, secondary, or tertiary alkyl of 1 to 7 carbon atoms.

2. A polymer according to claim 1 wherein the polymer is solution or emulsion polymer.

3. A polymer according to claim 1 wherein the polymer is natural rubber.

4. A polymer according to claim 2 wherein the polymer is solution polymerized polybutadiene.

5. A polymer selected from the group consisting of alpha mono-olefin polymers, natural rubber, and synthetic diolefin polymer rubber containing a stabilizing amount of the antidegradant mixture obtained by reacting about 2 parts alkylated m-cresol and about 1 part alkylated p-cresol, wherein the alkyl is secondary or tertiary alkyl of 4 to 12 carbon atoms, with an aliphatic aldehyde of 2 to 7 carbon atoms, said mixture containing at least about 40% of a compound of the formula r I A it ll J IIJ II wherein R is secondary or tertiary alkyl of 4 to 12 carbon atoms and X is straight or branched chain primary, secondary, or tertiary alkyl of 1 to 7 carbon atoms.

6. A polymer according to claim 5 wherein the polymer is solution or emulsion polymer.

7. A polymer according to claim 5 wherein the polymer is natural rubber.

8. A polymer according to claim '6 wherein the polymer is solution polymerized polybutadiene.

9. Solution polymerized synthetic diolefin polymer rubber containing a stabilizing amount of 2-[alpha,alpha- (4 hydroxy Z-methyl-S-tert-butyl phenyl)butyl]-6-tertbutyl-p-cresol.

10. Solution polymerized rubber according to claim 9 wherein the rubber is polybutadiene.

11. Solution polymerized synthetic diolefin polymer rubber containing a stabilizing amount of antidegradant mixture comprising about 10 to parts 2,2'-butylidenebis(6-tert-butyl-p-cresol), about 15 to part 4,4'-butylidenebis(6-tert butyl-m-cresol), and about 40 to parts 2 [alpha,alpha (4-hydroxy-2-methyl-5-tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol.

12. Solution polymerized rubber according to claim 11 wherein the rubber is polybutadiene.

References Cited UNITED STATES PATENTS 7/1951 Briggs et al.

2/1959 Webb 260-4595 8/1959 Palfreeman 260-4595 10/1965 Hinkamd 260-4595 11/1967 Cook 260-4595 HOSEA E. TAYLOR, ]R., Primary Examiner US. Cl. X.-R.

mg? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. I 3,505,287 Dat d April 7, 1970 Inventor) Evan Johnson Young and Charles Gene Summers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, lines 28-35, in the formula of claim S, cancel "OH" in the right hand ring next to CH and reinsert it one position downward so that the portlon of ,the formula 9 3 9 3 reading I reads -OH I l R R Signed and sealed this L th day of May 1971.

Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

